1. Field of the Invention
The present invention broadly relates to reference signal generating apparatus and, more particularly, is concerned with provision of such apparatus for generating elevation and azimuth reference signals to be utilized in demodulating a tracking error signal for making corrective adjustment of the position of a tracking conical scan radar antenna.
2. Description of the Prior Art
In a conical scan radar scheme, it is desired that the beam radiated by the antenna swing symmetrically around the target for precise tracking of the target. A low frequency portion of the signal received back by the radar receiver is used within the antenna servo system to provide a DC signal which contains information as to the tracking error or deviation from an exactly symmetrical circling position of the beam relative to the target. This tracking error signal is supplied to an elevation demodulator and an azimuth demodulator. Also, elevation and azimuth reference signals are generated and inputted to the respective demodulators to separate out the components of the tracking error signal which relate to elevation error and azimuth error. These separated components of the tracking error signal outputted by the respective demodulators are then used to drive servo motors for repositioning the antenna to track the target precisely in elevation and azimuth.
Heretofore, a reference signal generator of the armature and windings type has been used for generating the elevation and azimuth reference signals. This generator was mounted to the back side of the antenna assembly and was gear driven by the central nutator shaft of the assembly so as to rotate in one-to-one phase relationship with the angular rotational position of the nutator feed horn, during rotation of the nutator shaft, which produces the conical scan path of the antenna beam.
One disadvantage with this prior art arrangement is that the generator takes up a lot of space on the antenna assembly. Another disadvantage is that it is difficult to ensure that the generator is being driven by the gearing precisely in the desired phase relationship with the nutator feed horn.